1. Technical Field
The present invention relates to color image forming apparatuses that are suitable for application to a color printer, a color copying machine, or a multi functional product that has a photoreceptor drum and an intermediate image transfer belt, and carries out color misregistration correction processing by selecting either a color registration complex correction mode or a color registration single correction mode, or to color multi functional products of these types.
2. Description of Related Art
In recent years, tandem type color printers or color copying machines, or color multi functional products are being used very frequently. According to these types of color image forming apparatuses, in order to maintain at an optimum level the print quality (color reproducibility) of color images, the colors yellow (Y), magenta (M), cyan (C), and black (BK) that reproduce the colors R, G, and BK of the original document image are transferred onto an intermediate image transfer belt in a superimposing manner. In order to superimpose each of the colors Y, M, C, and BK with good reproducibility, it has become necessary to carry out actively color misregistration correction in an image forming unit (hereinafter referred to as a color misregistration correction mode).
Regarding the color misregistration correction mode, a color misregistration detection mark (hereinafter referred to as a register mark) for position detection formed on the intermediate image transfer belt or conveying member transfer belt is detected by a detection member (hereinafter referred to as a register sensor) for detecting color misregistration such as a reflection type sensor, etc., an amount of color misregistration of register marks of other colors with respect to a register mark of a reference color, fed back to different image forming units of the colors Y, M, and C so as to eliminate this amount of color misregistration, and good quality color images are obtained by correcting a laser writing timing.
Regarding these types of color copying machines, a color image forming apparatus has been disclosed in Patent Document 1. According to this color image forming apparatus, when a position deviation detection pattern is detected and color misregistration correction processing is executed based on a result of this detection, a pattern for density detection is formed in a non-image area, the pattern for density detection is detected, and a condition for creating an image for a position displacement detection pattern during color misregistration correction processing. When this type of color image recording apparatus is configured, it is possible to carry out color misregistration correction processing using the position displacement detection pattern whose density has been adjusted.
Patent Document 1: Unexamined Japanese Patent Application Publication No. 2005-91901 (Page 7, FIG. 9).
However, the following problems are present in color image forming apparatuses according to conventional examples as those seen in Patent Document 1.
(i). When carrying out color misregistration correction processing, a pattern for density detection is formed in the non-image area and the conditions for writing the position deviation detection pattern (a register mark) are determined by detecting this pattern for density detection. Therefore, even if it is possible to form a density adjusted register mark, it will be necessary to carry out again color misregistration correction at various image forming conditions at regular intervals due to an expansion or contraction of a writing unit, or the expansion or contraction of various types of drive rollers due to temperature conditions inside the apparatus.
(ii). In color misregistration correction operation, conventionally, when a timing of that color registration operation has come, irrespective of whether a paper size is small or large, either a job under printing operation is interrupted, or the color misregistration correction operation is made at the time of starting the print operation, and thereafter, again, the printing operation is started, and hence time was necessary only for carrying out the color misregistration correction operation. In particular, there was the problem that the color misregistration correction time became long in office applications, and the productivity of color copiers decreased.
(iii). However, when an apparatus is attempted to be configured in which the register mark is written in the non-image area outside the effective image area and the color misregistration correction processing is done continuously during the printing operation, it will be necessary to prepare a photoreceptor drum or an intermediate image transfer belt that is wider than the maximum size of the recording transfer sheets handled by that apparatus. Because of this, there was the problem that size reduction of the color copying machine was impeded and the cost went up by a large amount.
In view of this, the present invention is one that solves the above problems, and the purpose of the present invention is to provide a color image forming apparatus that not only shortens the color misregistration correction time on the whole compared to the color misregistration correction mode of the conventional method, but also increases the productivity of that apparatus.